Methylglyoxal (MG), also called pyruvaldehyde or 2-oxo-propanal (CH3—CO—CH═O) is the aldehyde form of pyruvic acid. It has two carbonyl groups, so it is a dicarbonyl compound. In organisms, methylglyoxal is formed as a side-product of several metabolic pathways. MG may be generated from 3-amino acetone, which is an intermediate of threonine catabolism, as well as through lipid peroxidation. However, the most important source is glycolysis, where methylglyoxal arises from non enzymatic phosphate elimination from glyceraldehyde phosphate and dihydroxyacetone phosphate, two intermediates of glycolysis. Since methylglyoxal is highly cytotoxic the body developed several detoxification mechanisms. One of these is the glyoxylase system. Methylglyoxal reacts with glutathione forming a hemithioacetal. This is converted into S-D-lactoyl-glutathione by glyoxylase I (GLO-I), and then further metabolised into D-lactate by glyoxylase II (GLO-II).
Why methylglyoxal is produced remains unknown, but several articles indicate that methylglyoxal is involved in the formation of advanced glycation endproducts (AGEs). In fact, methylglyoxal is proven to be the most important glycation agent (forming AGEs). In this process, methylglyoxal reacts with free amino groups of lysine and arginine residues of proteins forming AGEs (see FIG. 1). Other glycation agents include reducing sugars like glucose, galactose, allose and ribose.
Formation of methylglyoxal and related reactive carbonyl species (RCS) is closely linked to the rate of glycolysis and the presence of glycolytic intermediates. Hence, in conditions where there is increased glycolytic flux and an increased dependence on glycolysis for energy, the rate of methylglyoxal and RCS formation will also be increased. This has been shown to be the case in patients with diabetes mellitus, where complications such as nephropathy, neuropathy and retinopathy have been linked to increases in cellular levels of advanced glycation endproducts (AGEs). While diabetes has been the main area of research, new evidence is now emerging of the pivot role that RCS, in particularly methylglyoxal, plays in the progression and severity of various diseases. (see Table 1)
TABLE 1DiseaseSelected RefsAlzheimer's Disease 1-11Amyotrophic lateral sclerosis12, 13Cataractogenesis14, 15, 16Chronic renal failure and chronic or acute Uraemia17-25Cystic fibrosis26, 27Dementia with Lewy bodies28Diabetes and its complications38Ischaemia-reperfusion29Pre-eclampsia30Psoriasis31Rheumatoid arthritis and juvenile chronic arthritis32, 33Severe sepsis34, 35Systemic amyloidosis36Parkinson's Disease37Painful bowel disease
Sodium ion channels are integral membrane proteins that form ion channels, conducting sodium ions through the cell plasma membrane. They are classified according to the trigger that opens the channel for such ions, i.e. either a voltage-change (voltage-gated sodium channels) or binding of a substance (a ligand) to the channel (ligand-gated sodium channels). In excitable cells such as neurons, myocytes, and certain types of glia, sodium channels are responsible for the rising phase of action potentials. Sodium channels can often be isolated from cells as a complex of two types of protein subunits, α and β. An α-subunit forms the core of the channel. When the α-subunit protein is expressed by a cell, it is able to form channels which conduct Na+ in a voltage-gated way, even if β-subunits are not expressed. When β-subunits assemble with α-subunits the resulting complex can display altered voltage dependence and cellular localization. The α-subunit has four repeat domains, labeled I through IV, each containing six membrane-spanning regions, labeled S1 through S6. The highly conserved S4 region acts as the channel's voltage sensor. The voltage sensitivity of the channel is due to positive amino acids located at every third position. When stimulated by a change in transmembrane voltage, this region moves toward the extracellular side of the cell membrane, allowing the channel to become permeable to ions. The ions are conducted through a pore, which can be broken into two regions. The more external (extracellular) portion of the pore is formed by the “P-loops” (the region between S5 and S6) of the four domains. This region is the most narrow part of the pore and is responsible for its ion selectivity. The inner portion (cytoplasmic) of the pore is formed by the combined S5 and S6 regions of the four domains. See e.g. FIG. 2B.
Voltage-gated sodium channels have three types of states: deactivated (closed), activated (open), and inactivated (closed). Channels in the deactivated state are thought to be blocked on their intracellular side by an “activation gate”, which is removed in response to stimulation that opens the channel. The ability to inactivate due to a tethered plug (formed by domains III and IV of the alpha subunit), called an inactivation gate, that blocks the inside of the channel shortly after it has been activated. During an action potential the channel remains inactivated for a few milliseconds after depolarization. The inactivation is removed when the membrane potential of the cell repolarizes following the falling phase of the action potential. This allows the channels to be activated again during the next action potential.
There are a number of chemicals and genetic disorders which disrupt normal functioning of sodium channels and have disastrous consequences for the organism. Chemicals which can block sodium channels include Tetrodotoxin (produced by the puffer fish), Saxitoxin (produced by a dinoflagellate), Conotoxin (produced by cone snails), as well as the synthetic, local anesthetics, Lidocaine and Novocaine. Genetic disorders which effect the functioning of sodium channels, including Skaker (Sh) gene, human hyperkalaemic periodic paralysis (HyerPP), Episodic ataxia (EA), and Brugada syndrome.
In diabetes mellitus, neuropathy, which is one of three main major complications associated with the diseases, is frequently observed with patients exhibiting one or more types of stimulus-evolved pain, including increased responsiveness to noxious stimuli (hyperalgesia) as well as hyper-responsiveness to normally innocuous stimuli (allodynia). The underlying mechanism of persistent pain diabetic patients remains poorly understood and as such there are little or no effective therapeutic treatments which can either delay or prevent the onset of symptoms.
The present invention aims to provide means and methods for scavenging and/or antagonizing methylglyoxal and/or reactive carbonyl species (RCS), which allow an improved prevention and/or treatment of pain, in particular pain and/or hyperalgesia caused by or associated with methylglyoxal and/or reactive carbonyl species (RCS).